In various types of door locking devices, it is advantageous to differentiate between a situation where a dead bolt is projected into the strike opening and the case where a latch bolt is projected into the strike opening. In a mortise lock set wherein both a dead bolt and a latch bolt are utilized, the bolts are engaged by a keeper of the electric strike. If the strike becomes engaged, the keeper is released and the door may be pushed open. Upon returning the door to the locked position, it is necessary for the keeper to remain in the open position and then close up over the extended dead bolt to recapture the dead bolt prior to closing of the door. On the other hand, if the latch bolt was extended into the strike cavity, the keeper can return to the closed position automatically so that the returning latch bolt rides over the bevel of the keeper to thereby reengage the keeper.
It is therefore necessary to maintain the keeper open if the dead bolt were extended into the strike cavity so that the dead bolt can reenter the strike cavity prior to the keeper closing. If the dead bolt were extended and the keeper closed while the door was open, upon trying to reclose the door, the dead bolt would hit the top of the keeper and the door would not lock. Similarly, if the keeper were allowed to stay open when only the latch bolt was extended, the latch bolt could not pull the keeper into the locked position due to the bevel of the latch bolt as the latch bolt returned to the strike cavity. This situation would again prevent the door from locking.
A need has thus arisen for a simple and reliable device for sensing the presence of a dead bolt in a strike cavity to ensure that the keeper tracks the position of the dead bolt.